serial: 8250_fintek: UART dynamic clocksource on Fintek F81216H

The F81216H had 4 clocksource 1.8432/18.432/14.769/24MHzand  baud rates can
be up to 1.5Mbits with 24MHz. The register value and mask is the same with
F81866. But F81866 register address is F2h, F81216H is F0h.

We'll implements the dynamic clocksource in fintek_8250_set_termios().

Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_kernel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>